My pdfs with problems for CE characters are pdfs made directly from OCR by someone, no editing or correcting, they are old and have some unusual fonts embedded by the OCR software, custom encoding, so it's no wonder they can't show properly in duokan. What I mean is that's not a duokan bug. Kindle firmware also have trouble with them, showing spaces instead those CE characters. Although those pdfs were properly shown in older versions of duokan.

Every other pdfs are ok in duokan.

This is exactly my case with those three pdfs. Native Kindle OS shows blank spaces instead of ć,č,đ which makes the ebook entirely unreadable. Duokan detects characters in those places, but shows them awkwardly. Today I updated Duokan but still no change. I wrote to developers team yesterday, but there's no reply so far (I don't think they send emails to their "customers" but I do hope that they will have in mind this flaw with CE encoding while making future updates).

Does anyone know how to remove a little envelope on the top of the screen while Wi-Fi is turn on (it is a notice that I received an email). I suppose they sent me an email when I registered my Duokan account, but can't figure out how to open it and thus remove it from the screen.

It is a comment on the users of Open Source Software that think they do not need to obey the license terms.

oh... OK. This is also very important.
I just answered to "safe" as what this means to me.
But of course safety as of Open Source is another issue.
Hope to see the answer to that one myself.

Spoiler:

What I wanted to say is that we are not safe once we use internet. As internet is not so anonymous anymore as it was not so long ago. But again not the right answer because got wrongly the question from the beginning .

Duokan for me is better than original Kindle. Anyway, as mentioned @twobob if there is another open source software like Duokan, I will also immediately install open source software.
Duokan is kinda closed project.

The main problem on my Kindle powered by Duokan is non-translated language files. In every new version I do have more chinese words . Don't have anything against Chinese, but on my Kindle don't want to have any other than English words, reason is simple, i do not understand chinese.

● repair KT / KP Mobi manually turn the chapter can only turn to the second chapter;
● fix released K4 set the screensaver password Screensavers enter a password can not bring up the problem of the digital box;
● repair the wrong part of the machine time;
● Wifi occasionally connected on the repair part of the machine;
● repair mac machine plug kindle to generate hidden files Screensavers "I am not a touch screen" problem;
● repair K3/K4 books free catalog View catalog silent language;

If I switch from Duokan to Kindle, and after playing with Kindle and switch back to Duokan, the dictionary does not display words when I go next to the words. I need to select and click Dictionary, it only displays this way. I need to restart the Kindle to make it work. What might be the reason and how can I solve this? Thanks...